An Analysis of How Changes to Forest Structure Impact Measured Forest Roughness

Abstract:

The Savannah River Site (SRS) near Aiken, SC consists of a 900 km² area that is predominantly covered by a mix of pine and hardwood forest with small industrial areas which handle and process radioactive materials. The local US Forest Service maintains this forested region with management practices including thinning and clear-cutting. These activities can impact the meteorological measurements taken at the SRS meteorological monitoring network towers that support atmospheric transport modeling and emergency response. A study has been performed to understand how these disturbances to the forest environment, either from forest management activities or severe weather events, impact the measured roughness length of the forest used in atmospheric dispersion models and the flux footprint around the meteorological towers at SRS.

Changes to the forest structure over time have been identified using Google Earth imagery and the remotely-sensed NDVI. Meteorological data from sonic anemometers located on 61m towers across the SRS has been used to calculate the roughness length for wind sectors where forest structure changes have occurred in the periods prior to and following forest changes. Results demonstrate that while large-scale clear-cutting has tended to reduce the forest roughness, thinning activities and small clear-cut regions tends to increase forest roughness. The results of the assessment are expected to drive future forest management practices and timelines to ensure that there are not significant changes to the atmospheric transport behaviors that drive safety basis guidelines at the SRS.